Surface treatment process for aluminum alloy and aluminum alloy article thereof

ABSTRACT

A surface treatment process for aluminum alloy includes the steps of: providing an aluminum alloy substrate containing silicon element; evenly distributing the silicon element in the substrate by solution treating the substrate; removing the silicon element at/near the surface of the substrate by acid treating the substrate; forming a porous aluminum oxide film on the substrate by anodizing the substrate; and staining the aluminum oxide film. An aluminum alloy article treated by the process is also described.

BACKGROUND

1. Technical Field

The present disclosure relates to a surface treatment process foraluminum alloy and an aluminum alloy article treated by the process.

2. Description of Related Art

Aluminum alloys are widely used to manufacture housings of electronicdevices. The aluminum alloys are usually anodized and stained to presentcolorful appearances. However, the color of the aluminum alloy may notbe uniform due to the silicon element contained in the aluminum alloy.So, the silicon element is necessary to be removed from the aluminumalloy.

The current method to remove the silicon element is to treat thealuminum alloy using acid. However, treating the aluminum alloy usingacid can remove silicon element at/near the surface of the aluminumalloy, but not all the silicon element in the aluminum alloy. Commonly,the silicon element at/near the surface of the aluminum alloy has alower density than that of in the inner of the aluminum alloy. As aresult, despite removing the silicon element at/near the surface, mostof the silicon element in the inner would transmit to the surface of thealuminum alloy to affect the uniformity of the color.

Therefore, there is room for improvement within the art.

BRIEF DESCRIPTION OF THE DRAWING

Many aspects of the disclosure can be better understood with referenceto the following figure. The components in the figure are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the disclosure.

The figure is a cross-sectional view of an aluminum alloy article inaccordance with an exemplary embodiment.

DETAILED DESCRIPTION

A surface treatment process for an aluminum alloy may include thefollowing steps.

Referring to the figure, an aluminum alloy substrate 10 is provided. Thesubstrate 10 contains silicon element.

The substrate 10 is ultrasonically cleaned using absolute ethanol forabout 25 minutes (min) to about 35 min. Then the substrate 10 isair-dried for about 2 min to about 3 min.

The substrate 10 is solution treated. A chamber type electricalresistance furnace (not shown) is provided and set to have an innertemperature of about 495° C. to about 525° C. The substrate 10 ispositioned in the furnace to be solution treated for about 8 hours toabout 10 hours. During the solution treatment, the silicon element inthe substrate 10 takes place a transmission to evenly distribute in thesubstrate 10 along the thickness. That is, the solution treatment makesthe density of the silicon element in the substrate 10 consistent. Thus,the density of the silicon element at/near the surface of the substrate10 is greater than the density of the aluminum alloy which is notsolution treated.

The substrate 10 is removed from the furnace to be quenched in 5seconds. The quenching process is carried out by dipping the substrate10 in water for about 3 min to about 5 min. The water has a temperatureof about 20° C. to about 25° C.

The substrate 10 is acid treated to remove silicon element at/near thesurface of the substrate 10. The substrate 10 is dipped in an acidsolution for about 5 min to about 10 min The acid solution containsnitric acid and hydrofluoric acid in a volume ratio of about 8-10 :1-1.5. During dipping, the silicon element at/near the surface of thesubstrate 10 chemically reacts with the hydrofluoric acid to producesilicon tetrafluoride that can be dissolved in the acid solution,thereby the silicon element at/near the surface of the substrate 10 isremoved. After the acid treatment, the substrate 10, from the surface tothe depth of about 15 micrometers (pm) to about 25 μm, contains nosilicon element. The total content of the silicon element contained inthe substrate 10 decreases about 1.3% to about 1.65% after the acidtreatment. Since the silicon element has been evenly distributed in thesubstrate 10 after the solution treatment, the acid treatment in theembodiment can remove much more silicon element compared to theconventional acid treatment.

The substrate 10 is chemically polished to smoothen the surface andenhance the glossiness of the substrate 10. The chemical polishingprocess may include the following steps:

The substrate 10 is dipped in a first polishing solution having atemperature of about 70° C. to about 90° C. for about 20 seconds toabout 30 seconds. The first polishing solution contains sulfuric acidand phosphoric acid in a volume ratio of about 1-1.5 : 3-5. The sulfuricacid and the phosphoric acid ionize H⁺ to chemically react with thealuminum oxide that may formed on the surface of the substrate 10 in airto produce Al³⁺ and H₂O, thereby removing the aluminum oxide andsmoothening the surface of the substrate 10.

The substrate 10 is dipped in a second polishing solution having atemperature of about 60° C. to about 80° C. for about 20 seconds toabout 30 seconds. The second polishing solution contains nitric acid andphosphoric acid in a volume ratio of about 1-1.5 : 1-3. The phosphoricacid can chemically react with the aluminum contained in the substrate10 to produce an aluminum phosphate on the surface of the substrate 10,the aluminum phosphate then dissolves in the nitric acid, therebyenhancing the glossy of the substrate 10.

The substrate 10 is anodized. The anodizing process is carried out in asulfuric solution having a concentration of about 120 g/L to about 210g/L for about 5 min to about 65 min. The substrate 10 acts as an anode,a stainless steel is provided to act as a cathode. A voltage of about 20V to about 60 V is applied to the anode and cathode, producing anelectric current of about 2 A/dm² to about 6.5 A/dm² in the sulfuricsolution. During the anodizing process, the sulfuric acid is kept at atemperature of about 3° C. to about 30° C. After the anodizing process,an aluminum oxide film 12 is formed on the substrate 10 (see thefigure). The aluminum oxide film 12 has a thickness of about 5 μm toabout 12 μm, and contains no silicon element which would affect to thesubstantially staining to the aluminum oxide film 12. Further, thesolution treatment applied to the substrate 10 can also prevent thetransmission of the silicon element in the inner of the substrate 10 tothe surface of the substrate 10 to affect the substantial stainingprocess. The aluminum oxide film 12 defines a plurality of micro-pores121.

The aluminum oxide film 12 is stained using a colorant having aconcentration of about 0.2 g/L to about 4 g/L and a pH value of about4-10. The colorant may be xanthene dyes, methane dyes, coumarins dyes,cyanine dyes, stilbene dyes, or oxazine dyes. The pH value of thecolorant can be adjusted using an acetic acid, ammonia water, or sodiumhydroxide. The colorant has a temperature of about 30° C. to about 60°C. Staining the aluminum oxide film 12 may last for about 5 min to about20 min, allowing the micro-pores 121 to be completely filled by thecolorant.

A sealing treatment is applied to the aluminum oxide film 12, usingboiling water, vapor, nickel acetate, nickel sulfate, potassiumdichromate, or stearic acid. In the embodiment, boiling water isselected. The sealing treatment lasts for about 30 min to about 45 min.After the sealing treatment, a hydrated aluminum oxide film 14 is formedon the aluminum oxide film 12.

Referring to the figure, an aluminum alloy article 100 made by themethod above includes the aluminum alloy substrate 10, the aluminumoxide film 12, and the hydrated aluminum oxide film 14. The aluminumoxide film 12 is an anodic layer, and defines a plurality of micro-pores121 therein. The aluminum oxide film 12 has a thickness of about 5 μm toabout 12 μm. The aluminum oxide film 12 contains no silicon element,thus the aluminum oxide film 12 has a uniform color after being stained.

Specific examples of the surface treatment process are described below.The ultrasonic cleaning in these specific examples is as described aboveand always the same.

Example 1

In air drying the substrate 10: the substrate 10 was dried by a dryer(not shown) for 2 min.

In solution treating the substrate 10: the furnace had an innertemperature of about 525° C., the substrate 10 was positioned in thefurnace to be solution treated for about 8 hours.

In quenching the substrate 10: the substrate 10 was dipped in waterhaving a temperature of about 20° C. for 5 min.

In acid treating the substrate 10: the substrate 10 was dipped in theacid solution for 5 min The acid solution contained nitric acid andhydrofluoric acid in a volume ratio of 8:1. After the acid treatment,the total content of the silicon element contained in the substrate 10decreased about 1.3%.

In polishing the substrate 10: the substrate 10 was dipped in a firstpolishing solution having a temperature of about 70° C. for 20 seconds.The first polishing solution contained sulfuric acid and phosphoric acidin a volume ratio of 1:3. Then the substrate 10 was dipped in a secondpolishing solution having a temperature of about 60° C. for 20 seconds.The second polishing solution contained nitric acid and phosphoric acidin a volume ratio of about 1 : 1.

In anodizing the substrate 10: the anodizing process was carried out ina sulfuric solution having a concentration of about 130 g/L for about 15min. The substrate 10 acted as an anode, a stainless steel was providedto act as a cathode. A voltage of about 22 V was applied to the anodeand cathode, producing an electric current of about 2.3 A/dm² in thesulfuric solution. During the anodizing process, the sulfuric acid waskept at a temperature of about 20° C.

In staining the aluminum oxide film 12: the aluminum oxide film 12 wasstained using a xanthene dye having a concentration of about 4 g/L and apH value of about 5. The xanthene dye had a temperature of about 30° C.Staining the aluminum oxide film 12 lasted 5 min

In sealing the aluminum oxide film 12: boiling water was selected toseal the micro-pores of the aluminum oxide film 12 for 30 min.

Example 2

In air drying the substrate 10: the substrate 10 was dried by a dryerfor 2 min.

In solution treating the substrate 10: the furnace had an innertemperature of about 510° C., the substrate 10 was positioned in thefurnace to be solution treated for about 9 hours.

In quenching the substrate 10: the substrate 10 was dipped in waterhaving a temperature of about 15° C. for 5 min.

In acid treating the substrate 10: the substrate 10 was dipped in theacid solution for 5 min The acid solution contained nitric acid andhydrofluoric acid in a volume ratio of 10:1.5. After the acid treatment,the total content of the silicon element contained in the substrate 10decreased about 1.5%.

In polishing the substrate 10: the substrate 10 was dipped in a firstpolishing solution having a temperature of about 75° C. for 20 seconds.The first polishing solution contained sulfuric acid and phosphoric acidin a volume ratio of about 1:5. Then the substrate 10 was dipped in asecond polishing solution having a temperature of about 70° C. for 30seconds. The second polishing solution contained nitric acid andphosphoric acid in a volume ratio of about 1:1.

In anodizing the substrate 10: the anodizing process was carried out ina sulfuric solution having a concentration of about 180 g/L for about 20min. The substrate 10 acted as an anode, a stainless steel was providedto act as a cathode. A voltage of about 30 V was applied to the anodeand cathode, producing an electric current of about 3 A/dm² in thesulfuric solution. During the anodizing process, the sulfuric acid waskept at a temperature of about 20° C.

In staining the aluminum oxide film 12: the aluminum oxide film 12 wasstained using a xanthene dye having a concentration of about 3 g/L and apH value of about 6. The xanthene dye had a temperature of about 40° C.Staining of the aluminum oxide film 12 lasted 10 min.

In sealing the aluminum oxide film 12: boiling water was selected toseal the micro-pores of the aluminum oxide film 12 for 40 min.

Example 3

In air drying the substrate 10: the substrate 10 was dried by a dryerfor 3 min.

In solution treating the substrate 10: the furnace had an innertemperature of about 495° C., the substrate 10 was positioned in thefurnace to be solution treated for about 10 hours.

In quenching the substrate 10: the substrate 10 was dipped in waterhaving a temperature of about 20° C. for 5 min.

In acid treating the substrate 10: the substrate 10 was dipped in theacid solution for 10 min The acid solution contained nitric acid andhydrofluoric acid in a volume ratio of 9:1. After the acid treatment,the total content of the silicon element contained in the substrate 10decreased about 1.65%.

In polishing the substrate 10: the substrate 10 was dipped in a firstpolishing solution having a temperature of about 80° C. for 30 seconds.The first polishing solution contained sulfuric acid and phosphoric acidin a volume ratio of about 1:4. Then the substrate 10 was dipped in asecond polishing solution having a temperature of about 80° C. for 30seconds. The second polishing solution contained nitric acid andphosphoric acid in a volume ratio of about 1:2.

In anodizing the substrate 10: the anodizing process was carried out ina sulfuric solution having a concentration of about 200 g/L for about 60min. The substrate 10 acted as an anode, a stainless steel was providedto act as a cathode. A voltage of about 55 V was applied to the anodeand cathode, producing an electric current of about 5.5 A/dm² in thesulfuric solution. During the anodizing process, the sulfuric acid waskept at a temperature of about 5° C.

In staining the aluminum oxide film 12: the aluminum oxide film 12 wasstained using a xanthene dye having a concentration of about 1 g/L and apH value of about 5. The xanthene dye had a temperature of about 60° C.Staining the aluminum oxide film 12 lasted 20 min.

In sealing the aluminum oxide film 12: boiling water was selected toseal the micro-pores of the aluminum oxide film 12 for 35 min.

It is believed that the exemplary embodiment and its advantages will beunderstood from the foregoing description, and it will be apparent thatvarious changes may be made thereto without departing from the spiritand scope of the disclosure or sacrificing all of its advantages, theexamples hereinbefore described merely being preferred or exemplaryembodiment of the disclosure.

What is claimed is:
 1. A surface treatment process for aluminum alloy,comprising: providing an aluminum alloy substrate comprising siliconelement; evenly distributing the silicon element in the substrate bysolution treating the substrate; removing the silicon element at/nearthe surface of the substrate by acid treating the substrate; forming aporous aluminum oxide film on the substrate by anodizing the substrate;and staining the aluminum oxide film.
 2. The process as claimed in claim1, wherein solution treating the substrate is carried out by positioningthe substrate in a chamber type electrical resistance furnace having aninner temperature of about 495° C. to about 525° C. for about 8 hours toabout 10 hours.
 3. The process as claimed in claim 1, wherein acidtreating the substrate is carried out by dipping the substrate in anacid solution for about 5 min to about 10 min, the acid solutioncomprises nitric acid and hydrofluoric acid in a volume ratio of about8-10:1-1.5.
 4. The process as claimed in claim 3, wherein after the acidtreatment, the substrate comprises no silicon element from the surfaceof the substrate to the depth of about 15 μm to about 25 μm of thesubstrate, the total content of the silicon element contained in thesubstrate decreases about 1.3% to about 1.65%.
 5. The process as claimedin claim 1, wherein anodizing the substrate is carried out in a sulfuricsolution having a concentration of about 120 g/L to about 210 g/L forabout 5 min to about 65 min, the substrate acts as an anode, a stainlesssteel is provided and acts as a cathode, a voltage of about 20 V toabout 60V is applied to the anode and cathode, producing an electriccurrent of about 2 A/dm² to about 6.5 A/dm² in the sulfuric solution;wherein during the anodizing process, the sulfuric solution is kept at atemperature of about 3° C. to about 30° C.
 6. The process as claimed inclaim 5, wherein the aluminum oxide film has a thickness of about 5 μmto about 12 μm, the aluminum oxide film defines a plurality ofmicro-pores, and comprises no silicon element.
 7. The process as claimedin claim 1, wherein staining the aluminum oxide film is carried outusing a colorant having a concentration of about 0.2 g/L to about 4 g/Land a pH value of about 4-10, the colorant has a temperature of about30° C. to about 60° C., staining the aluminum oxide film last about 5min to about 20 min.
 8. The process as claimed in claim 7, wherein thecolorant is xanthene dyes, methane dyes, coumarins dyes, cyanine dyes,stilbene dyes, or oxazine dyes.
 9. The process as claimed in claim 7,wherein the pH value of the colorant is adjusted using an acetic acid,ammonia water, or a sodium hydroxide.
 10. The process as claimed inclaim 1, further comprising a sealing treatment to the aluminum oxidefilm using boiling water, vapor, nickel acetate, nickel sulfate,potassium dichromate, or stearic acid.
 11. The process as claimed inclaim 10, wherein a hydrated aluminum oxide film is formed on thealuminum oxide film after the sealing treatment.
 12. The process asclaimed in claim 1, further comprising a step of quenching the substrateafter the substrate being solution treated, the quenching process iscarried by dipping the substrate in water having a temperature of about20° C. to about 25° C. for about 3 min to about 5 min.
 13. The processas claimed in claim 1, further comprising a step of chemical polishingthe substrate before the substrate being anodized.
 14. The process asclaimed in claim 13, wherein the chemical polishing process comprisesthe following steps: the substrate is dipped in a first polishingsolution having a temperature of about 70° C. to about 90° C. for about20 seconds to about 30 seconds, the first polishing solution comprisessulfuric acid and phosphoric acid in a volume ratio of about 1-1.5:3-5;the substrate is dipped in a second polishing solution having atemperature of about 60° C. to about 80° C. for about 20 seconds toabout 30 seconds, the second polishing solution comprises nitric acidand phosphoric acid in a volume ratio of about 1-1.5:3-5.
 15. Analuminum alloy article, comprising: an aluminum alloy substrate, thesubstrate comprising no silicon element from the surface of thesubstrate to the depth of about 15 μm to about 25 μm of the substrate;an porous aluminum oxide film disposed on the substrate, the aluminumoxide film comprising no silicon element, and defining a plurality ofmicro-pores; and a hydrated aluminum oxide film disposed on the aluminumoxide film.
 16. The aluminum alloy article as claimed in claim 15,wherein the aluminum oxide film has a thickness of about 5 μm to about12 μm.